Current mirrors are generally used to provide an output current in proportion to an input current. For example, one type of current mirror may include an input P-channel field effect transistor and an output P-channel field effect transistor. The input current may be applied to a commonly connected gate and drain of the input transistor, which has its source connected to a voltage supply. The gates of the input and output transistors may be connected in common, and the source of the output transistor may also be connected to a voltage supply. The drain of the output transistor may be connected to provide the output current to a load device or other circuit. The input and output transistors may be sized to provide the output current a desired fraction greater than or less than the input current.
Prior art current mirror circuits, however, suffer several disadvantages. For example, prior art current mirror circuits are generally susceptible to breakdown of the gate oxide integrity of the input and output transistors. For example, the voltage signal to the input and output transistors may be greater than the gate oxide integrity of the input and output transistors. Where the gate and the drain of the input transistor are connected together, a source-to-gate voltage drop across the input and output transistors may exceed the gate oxide integrity of the input and output transistors. This is often possible due to transient circumstances and fault conditions that must be accounted for in the input signal received by the mirror circuit.